How is the Consumer Price Index (CPI) calculated?
The CPI is a “market basket” (collection) of goods and services that is used to measure changes in market prices. The data is collected from a series of interrelated samples. First, using data from the Census of Population, the Bureau of Labor Statistics (BLS) selects urban areas from which data on prices are collected. The Census of Population provides data on the number of consumers represented by each area selected as a CPI price collection area. Next, another sample (of about 14,500 families each year) serves as the basis for a Point-of-Purchase Survey that identifies the places where households purchased various types of goods and services. This information enables BLS to construct the CPI market basket of goods and services and to assign each item in the market basket a weight, or level of importance, based on total family expenditures. The final stage in the sampling process is the selection of the specific detailed item to be priced in each outlet. Price changes are weighted by
